Perspective Optical Illusion

Do you see anything when you gaze at this for 30 seconds and then look at a blank wall?

You may see an after image with moving specks when looking at the blank wall.

Explanation

This optical illusion has a lot of visual information in it with a high degree of contrast. This excites the visual system so much that it actually continues to fire visual clues to the brain after you have moved your focus away from the optical illusion.